214
H. WALTER AND E. STADELMANN
Frankincense, for which of old they went
Through plain and desert waterless, and faced
The Lion-haunted woods that edged the waste.
William Morris. The Earthly Paradise III
I. Introduction
The results of Walter's, early work formed the basis for the book "Die
Hydratur der Pflanze und ihre physiologischökologische Bedeutung (Untersuchungen über den osmotischen Wert; 1931)." The main conclusion
drawn from the experimental observations was that the fundamental problem for plants in arid zones is the maintenance of a sufficiently high degree
of hydration of the living protoplasm during periods of drought so that
the level of metabolism necessary to sustain life can be maintained. To
quantitate the degree of hydration Walter introduced a new term, the "hydrature," which is now defined thermodynamically as the "relative water
activity" in the cell (see Section VI). Meanwhile further investigations on
plant water relations in almost all of the deserts of the earth were made
by Walter (1936, 1939, 1960, p. 7, 1946, p. 8, 1968, p. 6). These investigations were based on concepts advanced in 1931.
This chapter will give a brief survey of Walter's results from four
decades of investigations on desert plant ecology. Data from less accessible
publications will often be mentioned, but it is not intended to include all
of the literature in this field. Parts of Sections X-XXI are taken from Walter and Kreeb (1970).
Since this chapter was written further contributions containing additional
material on water relations and ecophysiology of desert plants were published by Walter (1971, 1972, 1973a).
II. Rainfall and Water Supply of Desert Plants
The usual measurement of rainfall is given in millimeters and indicates
the amount of water in liters falling per square meter of ground surface.
Such measurement is by no means an indicator of the water supply of
the plants in arid regions. Rather it is necessary to consider also the density
of the plant cover and to know its transpiring surface also measured per
square meter of ground surface.
A very striking feature of all deserts is the low density of vegetation
which they support. Because of the low density of plant cover in deserts,
the bare ground or rock is widely exposed. This exposure becomes more
pronounced with decreasing rainfall and increasing dryness.
H. WALTER AND E. STADELMANN
Frankincense, for which of old they went
Through plain and desert waterless, and faced
The Lion-haunted woods that edged the waste.
William Morris. The Earthly Paradise III
I. Introduction
The results of Walter's, early work formed the basis for the book "Die
Hydratur der Pflanze und ihre physiologischökologische Bedeutung (Untersuchungen über den osmotischen Wert; 1931)." The main conclusion
drawn from the experimental observations was that the fundamental problem for plants in arid zones is the maintenance of a sufficiently high degree
of hydration of the living protoplasm during periods of drought so that
the level of metabolism necessary to sustain life can be maintained. To
quantitate the degree of hydration Walter introduced a new term, the "hydrature," which is now defined thermodynamically as the "relative water
activity" in the cell (see Section VI). Meanwhile further investigations on
plant water relations in almost all of the deserts of the earth were made
by Walter (1936, 1939, 1960, p. 7, 1946, p. 8, 1968, p. 6). These investigations were based on concepts advanced in 1931.
This chapter will give a brief survey of Walter's results from four
decades of investigations on desert plant ecology. Data from less accessible
publications will often be mentioned, but it is not intended to include all
of the literature in this field. Parts of Sections X-XXI are taken from Walter and Kreeb (1970).
Since this chapter was written further contributions containing additional
material on water relations and ecophysiology of desert plants were published by Walter (1971, 1972, 1973a).
II. Rainfall and Water Supply of Desert Plants
The usual measurement of rainfall is given in millimeters and indicates
the amount of water in liters falling per square meter of ground surface.
Such measurement is by no means an indicator of the water supply of
the plants in arid regions. Rather it is necessary to consider also the density
of the plant cover and to know its transpiring surface also measured per
square meter of ground surface.
A very striking feature of all deserts is the low density of vegetation
which they support. Because of the low density of plant cover in deserts,
the bare ground or rock is widely exposed. This exposure becomes more
pronounced with decreasing rainfall and increasing dryness.